By calling them "fees" or "voluntary contributions" or similar.

Taxes are only bad if a government extracts them at gunpoint. If a non-governmental force extracts them at... well, the gun is still there, I suppose, but hidden behind a layer of "If you don't pay, we sue, and if you don't pay after the lawsuit, the guns come out"... they're morally A-OK.

I only call it a "tax" as a shorthand, libertarians would not call it that. Rather they devise a system where, for example in the case of air pollution, there is no such thing as a public good, and instead of regulation and fines, potential air polluters would need to enter into a contract with the owners of the air in order to secure the right to pollute the air. And it pretty much goes downhill from there.

It's one of those things that might sometimes work okay on paper, but the trouble is that you can't actually try it out in practice due to the difficulty of assembling into a coherent community, a critical mass of people with the correct sort of deranged insanity to want to try it in the first place.

The solutions always involves either some kind of enforcing organization (ie - a government) or a hand wavy 'the market will provide' appeal to fervor.